As a memory device which forms an information processor, a dynamic random access memory (hereinafter, referred to as DRAM) has been used widely. As a technology for improving the reliability of the DRAM, a method for repairing defect bits is described in, for example, the following documents.
In the method disclosed in Japanese Patent Application Laid-Open Publication No. 2000-285695 (Patent document 1), defect bits are repaired in units of bit by substituting data of cells in an SRAM array on the same chip for data of cells of pose defects in a DRAM. In the method disclosed in Japanese Patent Application Laid-Open Publication No. 8-16486 (Patent document 2), an exclusive chip for repairing defect bits of a DRAM is provided in a DRAM module formed of a plurality of DRAM chips, and data is substituted in units of logic word line of the DRAM chip. In the method disclosed in a pamphlet of International Publication No. WO 02/45093 (Patent document 3), an SRAM is mounted in a DRAM chip, and normal word lines in the SRAM are substituted for a defect word line of the DRAM or that of the SRAM itself.